A digital tape recorder for recording and reproducing digital audio signals (referred to as PCM signals) by a pair of rotary heads is disclosed in, for example, U.S. Pat. No. 4,523,237 by the same applicant as the present invention. In such a digital tape recorder, sub codes such as the program number, the time code, and the like are recorded. In addition, PCM-IDs for identifying the sampling frequency, the number of channels, and the number or digitization bits of the PCM signal, the presence or absence of preemphasis, the characteristic thereof, and the like are recorded together with the PCM signal. In that apparatus, an error correction code is used such that the PCM signals of the amount to be recorded and reproduced by one rotary head are arranged in a matrix form, an error correction coding process C.sub.1 is performed for each PCM signal arranged in the vertical direction of the matrix arrangement, and an error correction coding process C.sub.2 is executed for each PCM signal arranged in the lateral direction of the matrix arrangement. The PCM signal which was subjected to an error correction coding process and the vertically arranged check symbol of the error correction code C.sub.1 are recorded and reproduced as a unit. Similarly, the PCM signal which was subjected to an error correction coding process and the laterally arranged check symbol of the error correction code C.sub.2 are also recorded and reproduced as a unit. To error correct the reproduced signal, decoding of the error correction code C.sub.1 (C.sub.1 decoding) is performed and the decoding of the error correction code C.sub.2 (C.sub.2 decoding) is then executed.
In order to easily interpolate the error symbols if uncorrectable errors occur, the even number designated data and the odd number designated data of the PCM signal are separately recorded in two adjacent tracks. With a pair of rotary magnetic heads, A an B in the case of the stereophonic PCM signals, the even number designated data Le of the L (left) channel and the odd number designated data Ro of the R (right) channel are recorded on the magnetic tape by the magnetic head A, and the odd number designated data Lo of the L channel and the even number designated data Re of the R channel are recorded on the magnetic tape by the magnetic head B. A pair of tracks formed by the respective magnetic heads in this manner are called an interleave pair. The data to be recorded in the tracks of the interleave pair have the same frame address in an additional code. Therefore, during reproduction, the interleave pair can be identified from the frame address. The reproduced data is subjected to the above described error correcting processes. The error corrected respective reproduced data of the interleave pair is synthesized and converted into the PCM signal.
A recording method wherein no guard band is provided between the tracks is used in order to raise the use efficiency of the magnetic tape. Namely, the lengthwise direction of the gap of the magnetic head A is different from that of the magnetic head B, thereby using azimuth loss to suppress the cross talk from the adjacent tracks.
As used herein, the term "PCM" signal (or signals) refers to the pulse code modulated audio signals which are to be recorded or reproduced; "block" of data refers to a unit amount of the recording data, in this embodiment 288 bits and may comprise PCM data, referred to as a "PCM data block" or sub code data, referred to as a "sub code data block"; and "symbol" which is eight bits. In order to keep track of the frames and blocks, addresses are assigned to them, e.g. a "frame address" refers to the address which identifies an interleave pair of tracks; a "block address" uniquely identifies a block of data.
As will be explained in further detail herein, in the foregoing rotary head type digital tape recorder, an error detection code using a simple parity is applied separately from the PCM signal to additional codes, such as a block address, to write blocks of the reproduced data into a buffer memory, the frame address indicative of the interleave pair, and the like, as will be explained in greater detail further in this specification in reference to the constitution of the data for the digital tape recorder. However, such an error detection code has the following drawbacks. Namely, the reliability of the result of the error detection is low. If an erroneous block address is reproduced, the reproduced data is written into the wrong block address. If an erroneous frame address is reproduced, the interleave pair are formed from unrelated data. Thus, there is the possibility that an annoying, abnormal sound can occur in the reproduced sound. Even if tee C.sub.1 and C.sub.2 decoding processes are performed using the error correction codes of the PCM signal, the occurrence of abnormal sounds cannot be completely prevented.
To overcome this problem, the same applicant of the present invention has previously proposed an apparatus for interpolating the error data if the frame addresses differ when one track is being traced. This apparatus is shown in U.S. Pat. No. 4,604,657 (European Patent Application No. 0,163,736 published on Dec. 11, 1985).
A rotary head type digital tape recorder can perform a variable speed reproducing operation in which the tape running speed is two or three or more times as fast as the recording mode tape speed. In a double speed reproducing mode or in a triple speed reproducing mode, in the case where the track TA recorded by the magnetic head A is scanned by the magnetic head B or where the track TB recorded by the magnetic head B is scanned by the magnetic head A, a reproduced signal can hardly be obtained because of the azimuth loss. The problem barely occurs if the reproduced signal of one of two tracks which were erroneously detected as the interleave pair can be sufficiently suppressed by the azimuth loss. However, even when the azimuths are not coincident due to tracking error, if the reproduced signal is obtained, or if the azimuths concerned with the reproduced signals from two tracks which were erroneously detected as the interleave pair coincide, a signal is reproduced in which PCM signals which are unconcerned with each other are alternately included with every reproduced digital word. Thus, there is the problem that annoying, abnormal sounds are reproduced.